The present invention relates to processes for Chemical Vapor Deposition (referred to as CVD, hereinafter).
CVD is a method enabling one to mass produce a metallic film of high quality, so it is practically used widely. A raw material used for the conventional CVD, however, is a gas at room temperature, such as silane, arsine, phosphine, diborane, ammonia, hydrogen sulfate, hydrogen selenide. Even in case of using a liquid, it is limited to a raw material which is very easy to vaporize, such as tetraethoxysilane (TEOS) or trimethyl gallium (TMG).
Recently, by the way, CVD is highly appreciated due to its high performance, so the method is used in a variety of technical fields. Especially, the development of usage of the method in the semiconductor industry is remarkable. In this industry, research is going on to use the following compounds that have never been considered to be used as a raw material for CVD: transition-metal compounds, alkali earth metal compounds or unstable metallic hydrogen compounds and compounds mixed with a metallic compound.
However, there are some problems to practically use these new raw materials.
The first problem is that such raw materials are unstable, have low can-stability, are extremely easy to decompose at vaporizing temperature and an addition product thereof is easy to remove.
The second problem is that most of the new raw materials that have not been practically used are solid at vaporizing temperature, so it is difficult to obtain a constant vaporizing amount because of effects of its grain shape and residues of the raw material in a reaction vessel.
The third problem is that each component of the reaction equipment cannot withstand the vaporizing temperature because the temperature is too high.
Here, it can be considered to solve the first problem by adding other substances to these new raw materials for stability.
For CVD, however, it has been never considered to add other substances whose boiling temperatures are different from the raw material, because it is necessary in the conduct of the CVD method to heat the vessel for raw materials, reduce gas pressure or bubble the carrier gas. Especially in the field of semiconductor production, ultra-high purity is needed, so the raw material is limited to a single substance or diluent gas with hydrogen and so on.
In recent some years, a flash vaporing method as a method to solve the above-mentioned second and third problems has been being proposed and studied. The flash vaporing method comprises steps of solving a solid raw material compound in an organic solvent to prepare a solution and continuously and simultaneously vaporing the solved solid compound and the organic solvent in the solution by sending the solution little by little to a heated vaporizer.
However, the organic solvent used for the flash vaporing method is not considered in relation to the raw materials, so the method can not solve the instability of the raw material compounds if the raw material compounds are unstable at the aimed vaporizing temperature. Also it has additional problems such as an effect to produce film by an organic solvent as an additional component and the necessity of addition of evacuation facilities.